Hi Popeye, and welcome to the cherub forums.
I am sure others will follow me with much advice, but to answer your specific questions the most recent designs (the 2005 rules boats) dont really fit into a sea/non sea category, arguably some might be marginally better than others but its pretty negligable.
I dont think I'm giving too much away when I say the current national champions boat traded for around the 6k mark, the boat in 2nd place is currenlty on the for sale pages for around 4k and as little as 2k will get you a perfectly sound planing machine. All the boats currently for sale offer tremendous value for money and the choice of which one depends as much on your budget, ability and aspirations as much as where you sail and the conditions.
IdeaI weight hovers around the 20-24stone mark (sorry too old for KG) although we have crews outside that perfectly capable, I suspect your ability wont be an issue with your previous (I have to say that as I have had 4 out of 5 of them !)
I sail in the south east too, be interested to know your local club and help you out a little more, if you want to contact me directly my details are on the contacts page..... cheers, Graham